This invention relates generally to the field of assembly and test of electronic or optical components, such as integrated optical devices, and in particular to edge detection.
The assembly and test of devices, such as integrated optical devices, require accurate alignment of components. For example, the assembly process for coupling optical fibers to optical chip components currently requires mechanical positioning to within 1 micron or less. The mechanical repeatability of chip placement equipment or manual loading of an optical chip into a test and assembly station, however, is much greater than 1 micron. Thus the position of the mating edges of a chip with respect to the mating fibers is known to an accuracy of no better than several microns. Consequently, additional steps must be taken to achieve sufficient accuracy in the relative positions of the components.
One approach is the use of a microscope together with manual positioning of the components. This approach requires trained and skilled operators. This is expensive and is subject to human error.
Another approach is the use of video microscopes in combination with image processing software and computer control of the positioning device. This type of equipment is expensive and relatively slow, and measurement accuracy is limited to a few microns.
The equipment used in these approaches tends to obstruct other processing equipment required to complete the assembly and test processes.
A further approach is the use of a light source and a light sensor to detect the edge of an object. The amount of light reaching the detector is reduced as the object obstructs the light path between the source and sensor. The accuracy of this approach is limited by the size of the detector and the accuracy to which the intensity of the light can be measured. Variations in the transfer efficiencies from the input current of the light source to the output current of the sensor introduce variability into the system, which limit the accuracy of this type of device. U.S. Pat. No. 5,187,375 to Masten describes an edge detection device with two detectors with the aim of mitigating this problem. However, in systems of this type, the accuracy is limited firstly because the sensor is responsive to ambient light and light from the source and secondly because the size of the detector is large compared to the sub-micron accuracy required. In the Masten detector, the sensor is much larger than the source and has a length of 100 mils (0.1 inches).
A still further approach is laser interferometry, in which the phase difference between a transmitted and a reflected beam of monochromatic light is used to determine a position. The approach requires complex equipment and is very expensive.
Accordingly, there is an unmet need in the art for an edge detector capable of determining the edge of an object to within a fraction of a micron.
Further, there is an unmet need for a non-contact positioning system that is capable of operating automatically and in real-time.
Still further, there is an unmet need for a non-contact positioning system that achieves sub-micron accuracy at a low cost.
The invention relates generally to a method and apparatus for edge detection with sub-micron accuracy. The edge detection apparatus comprises two single mode optical fibers with an optical path between them. One fiber is coupled to a laser light source, and creates a light beam. The other fiber is coupled to an optical power detector. The optical power reaching the optical power detector is determined by how much of the light beam is obscured by an object. Thus the position of an edge of the object may be determined from the optical power measured by the detector.
An object may be positioned automatically according to the optical power measured by the detector.